Wave Overtopping Rate Research Articles

Laboratory study on effect of vegetation in reducing wave overtopping under wind effect

Understanding and mitigating wave overtopping are crucial for hinterland safety, yet research primarily focuses on designing coastal structures, with limited attention to structural materials. As global warming intensifies coastal hazards, there is a growing need for resilient infrastructures. A hybrid infrastructure incorporating vegetation alongside concrete may offer a viable solution. In this study, we evaluated the effect of vegetation on wave overtopping reduction under strong winds through hydraulic model experiments simulating extreme storm conditions. The experiments were conducted under the simultaneous action of wind, waves, and vegetation using a two-dimensional wind tunnel flume and vegetation. A higher vegetation density was found to exponentially reduce the overtopping rate. Moreover, dense vegetation was demonstrated to be equivalent to raising the height of protective structures by at least 1.1 m. Furthermore, the increase in overtopping rate by the effects of wind can be compensated by the reduction effects of vegetation. Based on these investigations, an equation was proposed to predict the wave overtopping rate that considers the effects of both wind and vegetation. The results highlight the potential applicability of vegetated coastal protection in future coastal disaster prevention against extreme events with stronger winds and waves that may be induced by climate change.

Individual Wave Overtopping Volumes On Mound Breakwaters

Mound breakwaters are widely used to protect harbors from wave attack. Wave overtopping is a key parameter on the breakwater design, since it affects the hydraulic stability, the port operativity and also generates risks to the facilities, vehicles and pedestrians. The estimation of the mean wave overtopping rate, q[m3/s/m], has been extensively analyzed in the literature (see EurOtop, 2018 and Van Gent et al., 2007). However, the maximum individual wave overtopping volume, Vmax [m3/m], can be much larger than q[m3/s/m] and it is a better variable to evaluate the direct hazards. The prediction tools of q and Vmax are mainly based on laboratory tests, where q is registered much more easily than individual wave overtopping volumes. However, few of these studies detail the methodology to identify the number of overtopping waves and the associated individual wave overtopping volumes. The estimation of Vmax is usually made in literature (see Molines et al., 2019 and EurOtop, 2018) using a 2-parameter Weibull distribution (shape and scale factor) fitted with utility functions which consider the 10%, 30% or 50% of the highest individual wave overtopping volumes. The shape factor (b) is fitted with the laboratory measurements and the scale factor (A) is obtained by forcing the mean value of the Weibull distribution to be equal to the registered mean individual wave overtopping. In this study, a fully automatic detection methodology of the individual wave overtopping waves and volumes is developed using 2D physical tests. The performance of the 2-parameter Weibull and Exponential distributions to estimate Vmax is analyzed here with four utility functions to weight the data, f(u). The full findings of this study are available in Molines et al. (2019).

Improved prediction of wave overtopping rates at vertical seawalls with recurve retrofitting

This study investigates the reduction in overtopping discharge along a vertical seawall through the implementation of a recurve retrofitting. A comprehensive set of physical modelling experiments were undertaken in a laboratory-scale wave flume at the University of Warwick, to investigate the wave overtopping processes under both swell and storm wave conditions. The tests measured overtopping discharges for impulsive and non-impulsive wave conditions. The effects of geometrical design of recurve retrofitting on overtopping reduction are examined by four configurations with varying overhang length and recurve hight. The study revealed that the reduction in overtopping is primarily determined by the length of the overhang in the recurve wall, while the influence of the recurve height is limited. A longer overhang length results in a more substantial decrease in overtopping discharges on the seawall crest. The results also highlight the role of incident wave steepness and the crest freeboard on the overtopping mitigation performance of the recurve walls. A new enhanced methodology is proposed to predict the wave overtopping from vertical seawalls with recurve retrofitting., considering the effects of freeboard and wave steepness. The findings of this study provide new important insight in the role of retrofitting as a robust intervention to improve the wave overtopping mitigation performance of seawalls. The predictive empirical formulae proposed by this study facilitate readily and accurate estimation of overtopping rates as a function of retrofitting geometrical design, allowing for wider application of retrofitting solutions.

Estimate of Wave Overtopping Rate on Armoured Slope Structures Using FUNWAVE-TVD Model

In this study, the program was modified by adding the empirical formula of EurOtop (2018) to enable calculation of wave overtopping on armoured slope structures in the FUNWAVE-TVD model using the fully nonlinear Boussinesq equation. The validity of the modified numerical model was verified by comparing it with CLASH data and experiment data for the rubble mound structure. This model accurately reproduced the change in wave overtopping rate according to the difference in the roughness factor of the armoured block, and well reproduced the rate of decrease in wave overtopping rate due to the increase in relative freeboard. The overtopping rate of the armoured slope structures showed significant differences depending on the positioning condition of the armoured blocks. When Tetrapods were placed with regular positioning, the overtopping rate increased significantly compared to when they were placed with random positioning, and it was consistent with when they were placed with Rocks. Meanwhile, when rocks were placed in one row, the wave overtopping rate was greater than when rocks were placed in two rows, which is believed to be due to the influence of the roughness and permeability of the structure’s surface.

EVALUATION OF OVERTOPPING MODEL PERFORMANCE USING NOVEL EXPERIMENTAL DATA FROM INDUSTRIAL DESIGN PROJECTS

A critical requirement in successfully planning to mitigate wave overtopping is the ability to predict the frequency at which coastal defences will be overtopped. Many empirical formulae have been developed to predict wave overtopping rates for specific structural typologies and hydrodynamic conditions. More recently, Machine Learning methods have been deployed in an effort to make models that generalize across a wide range of structures and environments. A critical enabling factor has been the compilation of systematically parameterized physical model data, culminating in the EurOtop extended database. Practitioners now have the luxury of choosing between multiple, high-quality models. In addition, given the rapid advancement in usability of modern Machine Learning frameworks, training their own bespoke models is an increasingly realistic option. What is now needed is more information, showing how these models perform on unseen data, in a practical design context, in order to continue to refine guidance around their use.

EFFECT OF TANDEM BREAKWATER ON PRESSURE REDUCTION ON VERTICAL SEAWALL

There is an urgent need to develop methodologies to upgrade and retrofit existing coastal structures to retain their functionality in the scenario of changing climate. It is noticed that higher wave loads cause structural damage and increase wave overtopping rates, resulting in coastal flooding and inundation. Hard structures like seawalls can be reinforced by constructing a submerged breakwater in tandem with the seawall to adapt to the increased wave action due to climate change. Wave height attenuation, overtopping volume, and wave pressure or forces on structures are the important design parameters to be considered for the design of upgradation methods for coastal structures to withstand future climatic events. There are few works available in the literature focused on this direction. In the present study, we focus on pressure reduction on seawall due to the presence of a submerged breakwater in tandem with the seawall. Numerical simulations were carried out using a CFD-based numerical tool REEF3D to understand the effect of a submerged breakwater on wave pressure reduction on the seawall. The work also includes a validation study where the numerical results based on the present work are compared with the experimental studies from the literature.

Wind Effects on Wave Overtopping at a Vertical Sea Defense

The wind effect on the efficiency of a coastal defense structure is studied in this paper. It is normally assumed that the strength of the wind impact is characterized by the impulse parameter. If it is lower than a certain value, the wind is expected to have a dominant effect on the wave overtopping rate. In contrast to the regular observation, this study reports a new regime of wave overshoot when a low value of the impulse parameter does not lead to increased importance of wind. It is argued that the new regime appears due to the triplet instability previously studied by others. The variation of the standing wave height and the overshooting jet between the sequential cycles results in independence of the overtopping rates of the wind speed.

Physical Model Test for Wave Overtopping for Vertical Seawall with Relatively Steep Bottom Slope for the Impulsive Wave Condition

Wave overtopping rate is one of the most important design parameters for coastal structures. In this study, the physical model tests for measuring the wave overtopping have been conducted with the foreshore slope in front of the seawall. The bottom seabed for the coastal road area was fabricated at the wave flume for two areas in the East sea areas. The wave overtopping rate was measured for various water depths and wave conditions in each coastal area. In particular, the impulsive wave conditions were compared with the previous research and the similar trends of wave overtopping was observed. It could be known that the effect of foreshore slope was significant and should be concerned for applying theses formula like EurOtop.

Development of a typhoon wave overtopping prediction model based on an artificial neural network

In this study, an artificial neural network (ANN) model for the typhoon wave overtopping was developed using the database by a numerical wave flume simulation. The developed ANN model is effective for saving calculation time largely. The accuracy of the model is also approached to over 95% of the numerical simulation. This accuracy was evaluated by the correlation coefficient and the root mean square error with the target data of the numerical simulation and output of the ANN model. This model quickly produces the mean wave overtopping rate, maximum wave run-up height, maximum wave overtopping depth and velocity at the middle point in the coastal road without high-fidelity numerical model and high-computing resources. It means that the typhoon warning system including the ANN models is powerful and useful rather than only the monitoring warning system currently in use.

Hydraulic and Numerical Tests on Wave Overtopping for Vertical Seawall with Relatively Shallow and Steep Sloped Water Depth

In Korea, the hydraulic model tests for measuring the wave overtopping have been almost conducted with no bottom slope or single slope condition in Korea. In this study, the bottom seabed for the coastal road area was fabricated at the wave flume and the wave overtopping was measured. The overtopping rate was also measured with the numerical modelling by OLAFoam. The measuring data were compared with EurOtop manual. It could be known the the influence of the foreslope in front of the vertical wall was significant and the these effects should be concerned when designing the coastal structures. And also it could be known that OLAFoam could be used to predict the wave overtopping rate for the complex bottom topography.

Numerical simulation of waves overtopping over impermeable sloped seadikes

In this study, a numerical model of white water overtopping of regular waves over an impermeable seadike is developed using the Volume of Fluid (VOF) method based on Reynolds-Averaged Navier-Stokes (RANS). The numerical model is favored due to the challenges in experimentally quantifying the hydrodynamic features of overtopping flow, particularly at the beginning of the crest, as well as the uncertainty in various design formulae estimating wave overtopping rates. Such uncertainties are caused by insufficient wave height statistics in irregular wave trains, which may be addressed by taking into account overtopping rates of regular wave tests as well as robust statistical distributions of wave heights and periods. For this purpose, first, by ensuring the numerical model's validity, effective hydraulic and structural parameters on regular waves overtopping are investigated and their dimensionless forms are determined using the dimensional analysis method. Based upon the developed model and in-depth estimation of dimensionless parameters' effect on overtopped layer thickness, the overtopping velocity at the beginning of the crest, and the average overtopping rate, the wave breaker type is determined to be highly effective at reducing overtopping parameters. By analyzing the numerical model run results, formulae are proposed to predict the layer thickness, the wave overtopping velocity at the beginning of the crest, and the average wave overtopping rate independent of the flow characteristics on the slope seaward. Comparing the results of the proposed formulae with other researchers highlights the appositeness and reliability of the numerical simulation and the proposed formulae. Using the obtained formulae of layer thickness and overtopping velocity, along with consideration of sliding, toppling, and floating criteria, appropriate criteria are proposed to control the overtopping safety for pedestrians and vehicles. Moreover, compared to the average overtopping rate, the overtopping velocity and layer thickness parameters are found to be more appropriate in investigating the overtopping risk for pedestrians and vehicles.

Impacts of sea level rise on wave overtopping rates around the coast of England

There is unequivocal evidence that global sea levels are rising. It is therefore inevitable there will be socioeconomic impacts as a result of this. To aid mitigation, and the implementation of adaptation measures, it is vital the magnitude of the potential impact is quantified. Current approaches in the UK make simplifying assumptions regarding the relationship between present-day and future economic damage relating to coastal flood risk. The analysis undertaken here supports studies of an improved impact of sea level rise by providing national-scale estimates of changes in wave overtopping rates and flood defence overflow rates, as a result of different amounts of sea level rise. The analysis involves the application of components of an existing risk-based coastal flood risk analysis method. A subset of almost 600 flood defence assets around the country has been analysed for sea level rise rates up to 1 m. The resulting analysis shows that, on average, the wave overtopping rate increases by up to 150 times above present-day rates for lower return periods and by up to five times for higher return periods. This differential arises as a result of non-linearities in overtopping rates with increasing extreme sea levels.

Comparison of solitary wave overtopping characteristics between vertical and wave absorbing revetments

In this study, the wave overtopping characteristics of the solitary wave were investigated in the vertical revetment (VR) and the wave absorbing revetment (WAR) through hydraulic experiment and numerical analysis. In the case of WAR, the horizontal flow velocity significantly increased on the crest as the solitary wave passed through the inclined wave absorbing region and the flow cross-sectional area decreased. In terms of VR, the water level rose and the vertical flow velocity developed, as it was blocked by the impermeable vertical wall and the wave overtopping progressed. As a result, the WAR and VR wave overtopping rates were larger under the conditions of a relative solitary wave height of <0.272 and >0.272, respectively. Furthermore, the wave overtopping discharge per unit time was calculated in VR and WAR by applying the effective period of solitary waves, and a dimensionless overtopping formula for solitary waves was proposed.

Numerical study on the hydrodynamic performance of a revetment breakwater in the South China Sea: A case study

The South China Sea (SCS) is an important channel for international trade and energy transportation of China, which is of great significance for strategic and economic development. To prevent the reclaimed reef islands in the SCS from wave scouring and impacting, a large number of revetment breakwaters have been constructed at the margins of those reclaimed artificial lands. It is of great engineering importance to evaluate the ability of those revetment breakwaters withstanding the impact of ocean waves. In this study, a series of hydrodynamic numerical simulations are carried out to study the performance of the revetment breakwaters built on the reclaimed reef islands in the SCS adopting the actual terrain and real size of structure. It is found that under the fortified wave condition, the peak value of wave impact imposed on the caisson can reach up to 43.5 kPa, and the peak rate of wave overtopping is 3 m3/s per meter. However, under the condition of extremely higher waves, the peak wave impact could reach 102.2 kPa, and the overtopping rate is 11.5 m3/s per meter. The significantly increased wave impact and wave overtopping are harmful to the stability of those revetment breakwaters and the ecological environment on the reclaimed reef islands. Meanwhile, the relationship between the wave height, wave period, the initial seawater level and the water level setup on reef flat, wave impact on the revetment breakwaters, water overtopping is parametrically studied. The results of this study should own some reference significance for the design, post-construction maintenance, and safety evaluation of the revetment breakwaters built on the reclaimed reef islands in the SCS.

Estimate of Wave Overtopping Rate on Vertical Wall Using FUNWAVE-TVD Model

This study established a numerical model capable of calculating the wave overtopping rate of coastal structures by nonlinear irregular waves using the FUNWAVE-TVD model, a fully nonlinear Boussinesq equation model. Here, a numerical model was established by coding the mean value approach equations of EurOtop (2018) and empirical formula by Goda (2009), and adding them as subroutines of the FUNWAVE-TVD model. The verification of the model was performed by numerically calculating the wave overtopping rate of nonlinear irregular waves on vertical wall structures and comparing them with the experimental results presented in EurOtop (2018). As a result of the verification, the numerical calculation result according to the EurOtop equation of this model was very well matched with the experimental result in all relative freeboard (Rc/Hmo) range under non-impulsive wave conditions, and the numerical calculation result of empirical formula was evaluated slightly smaller than the experimental result in Rc/Hmo &lt; 0.8 and slightly larger than the experimental result in Rc/Hmo &gt; 0.8. The results of this model were well represented in both the exponential curve and the power curve under impulsive wave conditions. Therefore, it was confirmed that this numerical model can simulate the wave overtopping rate caused by nonlinear irregular waves in an vertical wall structure.

Experimental study of wave overtopping at rubble mound seawalls

Seawalls play a significant role in protecting coastal areas against wave attack and flooding. The accurate estimation of wave overtopping at seawalls is therefore crucial to adequately protect people and infrastructure in these regions. In this study, the mean wave overtopping rate at rubble mound seawalls was investigated through 140 small-scale physical model tests which adds to the limited existing data for this structure type in the extended CLASH database called EurOtop (2018). The combined dataset is used to evaluate the prediction skill of existing empirical formulae and to identify their limitations. The role of wave steepness on the mean overtopping rate is closely examined as it has not yet been considered properly in the EurOtop (2018) formulation. A new formula was derived using dimensional analysis and physical justifications of the overtopping phenomenon. The formula was found to provide a 40% decrease in RMSE in comparison to that of the EurOtop (2018). In addition, the new formula yields a BIAS ≈0, a significant improvement compared to −0.38 (non-dimensional discharge) of the EurOtop (2018) formula. The proposed formula has a simple form where non-dimensional overtopping discharge depends only on the relative crest freeboard and wave steepness, which were found to be the most important variables based on a sensitivity analysis.

Full-scale experimental study on wave reflection and run-up at stepped revetments

Stepped revetments are especially suitable in urban areas as they effectively limit wave overtopping whilst offering recreational benefits. A deeper understanding of wave-structure interactions facilitates optimised stepped revetment designs. Wave reflection and wave run-up processes also indirectly provide insights in the wave energy dissipation of stepped revetments. Only few studies have focused on wave reflection from stepped revetments, while the wave run-up process on stepped revetments was studied widely, yet only with small-scale wave flume tests and mostly with regular waves. As the wave overtopping rates in small-scale wave flume tests underestimate those measured in full-scale experiments, these studies are likely affected by scale. This paper investigates wave reflection from and wave run-up on stepped revetments by means of full-scale flume experiments. Two cross-sections, each with a slope of 1:3, were studied with uniform step heights of 0.17 m and 0.50 m. It was found that previous small-scale studies underestimate relative run-up heights by 31–51%. Empirical formulae were derived to estimate wave reflection coefficients and wave run-up heights of stepped revetments. Wave reflection and run-up processes are described and provide further insight in the functioning of stepped revetments.

Wave Overtopping Rate on Vertical Seawall with Deformed Wave Dissipating Work

Araki, S.; Kotake, Y.; Kubota, S.-I.; Shibutani, Y.; Kawauchi, Y., and Yamamoto, F., 2021. Wave overtopping rate on vertical seawall with deformed wave dissipating work. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 176–180. Coconut Creek (Florida), ISSN 0749-0208. This paper describes the variation in wave overtopping rate with deformation of wave dissipating work. Slight deformation of wave dissipating work is expected to cause no significant increase in wave overtopping rate. A series of hydraulic experiment was conducted to measure the wave overtopping rate at a vertical seawall with deformed wave dissipating work. The experiment shows that the deformation of wave dissipating work does not necessarily cause a drastic increase in the wave overtopping rate. Although a procedure for estimating the wave overtopping rate is proposed, the results show that the procedure needs to be improved.

Experimental Study on Hydraulic Performance of Tiecell Caisson Breakwater with Wave Chamber

Kim, I.-C.; Park, K., and Kang, T.-W., 2021. Experimental study on hydraulic performance of tiecell caisson breakwater with wave chamber. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 81–85. Coconut Creek (Florida), ISSN 0749-0208. Recently, a perforated caisson breakwater with tiecell blocks was developed to improve a water affinity and people's safety of a rubble mound armoured by tetrapods. In this study, hydraulic model tests were performed to examine the hydraulic performance of a non-porous and a tiecell caissons with perforated blocks attacking wave against a small fishery harbor near Busan. The model test results show that the tiecell caisson is more effective in dissipating wave energy under normal wave conditions and in reducing wave overtopping rates under design wave conditions than the non-porous caisson. It is found that the horizontal wave forces acting on the tiecell caisson show slightly more large than the non-porous caisson due to the impulsive force generated in the wave chamber.

Applicability of Disaster Scale Criteria for Swell-Like Waves Based on Wave Overtopping Predictions

Lee, S.-Y.; Kim, D.-H.; Kim, D.-S.; Kim, H.-J.; Jeong, Y.-H.; Hong, S.-J., and Lee, H.-Y., 2021. Applicability of disaster scale criteria for swell-like waves based on wave overtopping predictions. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 226–230. Coconut Creek (Florida), ISSN 0749-0208. In this study, a wave overtopping prediction system was established for 10 major ports adjacent to 10 testbeds in South Korea, and a qualitative assessment of the system's reproducibility was performed through field surveys. The system estimates the probability of wave overtopping hazards, which is required for responding to disasters caused by swell-like waves. Wave overtopping prediction requires information on artificial structures in the major ports near the testbeds, swell-like wave predictions, and wave overtopping rate calculations. The threshold for defining wave overtopping hazards that can affect the hinterland, facilities, and residents in coastal areas was set to 0.01 m3/s/m, in accordance with EurOtop standards (Pullen et al., 2018) and the Korean Ministry of Oceans and Fisheries. The results of this study can be used to facilitate decision-making by providing qualitative estimations of wave overtopping hazards at various levels. By comparing the results to standard values, the risk of swell-like waves in testbeds along the East Sea coast can be determined. The proposed system can be used to avoid casualties and property damage in the event of a wave-overtopping disaster.